1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to seismic sources having a steerable submersible float configured to control positions of individual seismic sources attached to the steerable submersible float and related methods.
2. Discussion of the Background
Marine explorations investigate and map the structure and character of geological formations under a body of water using reflection seismology. Reflection seismology is a method of geophysical exploration to determine the properties of earth's subsurface, which are especially helpful in the oil and gas industry. Marine reflection seismology is based on using a controlled source of energy that sends the energy into the earth. The depth and horizontal location of features causing reflections are evaluated by measuring the time it takes for the reflections to arrive at plural receivers. These features may be associated with subterranean hydrocarbon reservoirs.
A traditional marine exploration system is illustrated in FIG. 1. A vessel 100 tows a seismic source 102 and an array of seismic receivers 104 provided on streamers 106. The streamers may be disposed horizontally, i.e., lying at a constant depth relative to a surface 108 of the water. The streamers may be disposed to have other than horizontal spatial arrangements. The seismic source 102 is configured to generate a seismic wave 110, that propagates downward toward the seafloor 120 and penetrates the formations under the seafloor until eventually it is reflected at discontinuity locations 122. The reflected seismic wave 130 propagates upward until it is detected by one of the receivers 104 on the streamer 106. Based on the data collected by the receivers, an image of the subsurface formation is generated by further analyses of the collected data.
A seismic source array typically includes plural individual source elements grouped in one or more sub-arrays. The individual source elements may be distributed in various patterns, e.g., circular, linear, at various depths in the water. Maintaining relative horizontal positions and depths of the seismic sources and the streamers according to a desired geometry is desirable in order to ensure accuracy and resolution of the extracted information. However, achieving this type of control has proven challenging due to marine currents and other disturbances, including, for example, the trailing air bubbles that occur when compressed air guns are discharged.
For example, in U.S. Pat. No. 7,804,738 to Storteig et al., deflectors coupled via cables and ropes to a towed source provide a mechanism to control the horizontal position. However, this mechanism has an undesirable slow reaction time when necessary to adjust the position of the sources. In U.S. Pat. No. 7,415,936 to Storteig et al., besides deflectors, winched cables are used to steer the towed source. This mechanism also exhibits a slow reaction time. FIG. 2 illustrates a marine exploration system 200 in which two vessels 210 and 220 sail on correlated trajectories at a distance D from one another, while pulling a rope or cable 230 to which plural arrays of individual sources 240a, 240b, 240c and 240d are attached to be towed at a distance C from one another. Thus, in order to correct the position of a source, either the towing vessel needs to change its trajectory or winches need to be used. This mechanism also has an undesirably slow reaction time.
In U.S. Patent Application Publication No. 2010/00226204 to Gagliardi et al., a source useable for arctic marine exploration is towed underwater, the source including a floatation device with depth control via plural buoys. The source has no means of controlling its horizontal position.
To summarize, the conventional sources and means of controlling position and depth thereof have a slow reaction time and limited maneuverability.
Accordingly, it would be desirable to develop mechanisms and methods to more efficiently and fast steer and position a seismic source for marine exploration.